<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <!-- 新 Bootstrap4 核心 CSS 文件 -->
    <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/css/bootstrap.min.css">

    <!-- jQuery文件。务必在bootstrap.min.js 之前引入 -->
    <script src="https://cdn.staticfile.org/jquery/3.2.1/jquery.min.js"></script>

    <!-- bootstrap.bundle.min.js 用于弹窗、提示、下拉菜单，包含了 popper.min.js -->
    <script src="https://cdn.staticfile.org/popper.js/1.15.0/umd/popper.min.js"></script>

    <!-- 最新的 Bootstrap4 核心 JavaScript 文件 -->
    <script src="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script>
</head>
<body>


<div id="demo" class="carousel slide" data-ride="carousel">
    <!-- 指示符 -->
    <ul class="carousel-indicators" style="margin-bottom: 120px">
        <li data-target="#demo" data-slide-to="0" class="active"></li>
        <li data-target="#demo" data-slide-to="1"></li>
        <li data-target="#demo" data-slide-to="2"></li>
    </ul>

    <!-- 轮播图片 -->
    <div class="carousel-inner">
        <div class="carousel-item active">
            <img src="https://static.runoob.com/images/mix/img_fjords_wide.jpg">
        </div>
        <div class="carousel-item">
            <img src="https://static.runoob.com/images/mix/img_nature_wide.jpg">
        </div>
        <div class="carousel-item">
            <img src="https://static.runoob.com/images/mix/img_mountains_wide.jpg">
        </div>
    </div>
    <!-- 左右切换按钮 -->
    <div >
        <a class="carousel-control-prev" href="#demo" data-slide="prev" style="margin-bottom: 100px">
            <span class="carousel-control-prev-icon"></span>
        </a>
    </div>
    <div>
        <a class="carousel-control-next" href="#demo" data-slide="next" style="margin-right: 0px;margin-bottom: 100px">
            <span class="carousel-control-next-icon"></span>
        </a>
    </div>
</div>
</body>
</html>